Content Resizing: Fix "Shorten" action for CJK languages

[i-anubhav-anand]

What?

Closes #578

Fix the "Shorten" action in Content Resizing so it works for CJK content (Chinese, Japanese, Korean).

Why?

The minimum-length check before shortening uses count(text, 'words'), which returns 0 for CJK text (no word separators). Any CJK paragraph block triggers the "Text is too short to shorten further" error regardless of actual content length.

How?

• Added a CJK_REGEX (same pattern as the fix for Content Classification: Make character count locale-aware #571) to detect CJK content at runtime.
• When CJK content is detected, the minimum is checked against 'characters_excluding_spaces' with a threshold of SHORTEN_MIN_CHARS = 10 instead of SHORTEN_MIN_WORDS = 5 words.
• The word-diff badge in the result modal also adapts to character counting for CJK content, so the "+N words" / "−N words" label reflects character deltas instead.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): claude-sonnet-4-6
Used for: Implementation assistance; code reviewed and verified by me.

Testing Instructions

1. Set site language to Japanese (Settings → General → Site Language).
2. Open a post, paste あああああああああああ ~3 times into a paragraph block.
3. From the AI toolbar dropdown on the block, click "Shorten".
4. Confirm the modal opens and a suggestion is generated (previously showed an error notice "Text is too short to shorten further").
5. With English text of fewer than 5 words, confirm the error still shows correctly.

Screenshots or screencast

N/A — the change is functional (Shorten action no longer errors on CJK content).

Changelog Entry

Fixed - Content Resizing: the "Shorten" action now works for CJK languages (Chinese, Japanese, Korean) by checking character count instead of word count when CJK text is detected.

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[dkotter]

One, this is opened against trunk, not develop. Two, this seems to just be a duplicate of #715 which we already ask to be closed as it itself was already a duplicate. As such, closing this out but let me know if I'm missing something here